Temperature gradients within and adjacent to the North Island volcanic belt

Abstract

Temperature gradients have been measured in 44 drillholes within the North Island volcanic belt. New Zealand, and in 4 further holes adjacent to this region. Temperature gradients ranged widely from zero, or slightly negative values to +815°c/km. This variation is attributed to the existence of convective hydrothermal systems within the volcanic belt. Heat flow values for five drillholes for which adequate lithologic data were available ranged from 28 to 113 mW 1m'.

Three-dimensional model of the deep geothermal resources in the Taupo–Reporoa Basin, New Zealand

“…For regions adjacent to, but outside the TVZ, Thompson (1977) states that all of the data are consistent with a vertical temperature gradient of approximately 30°C/km. Therefore in the exterior region a thermal conductivity of 3 W/mK was used and a heat flux of 0.09 W/m 2 is distributed uniformly over the base boundary in order to represent this level of background terrestrial heat flow.…”

A three dimensional numerical model of the Waiotapu, Waikite and Reporoa geothermal areas, New Zealand

“…Boundary conditions 3.1.1. Base Thompson (1977) states that in regions adjacent to, but distant from the TVZ, most temperature logs are consistent with a vertical temperature gradient of approximately 30°C/km. A typical, relatively high, thermal conductivity 2.5 W/m K was used in the model and therefore a heat flux of 0.08 W/m 2 was assigned to the base boundary of the model to represent the background terrestrial heat flow.…”

Convective Flows in a TVZ-like Setting with a Brittle/Ductile Transition

“…On the lower boundary there is no fluid flow, and the adopted thermal conductivity of 2.5 W/m/K and the assumption of a steadystate conductive geothermal gradient of 20 • C/km for tectonically stable continental crust (e.g., Ranalli 1986) is met by imposing a laterally constant basal heat flux of 50 mW/m 2 . For the TVZ region 50 mW/m 2 is a low heat flux, but falls within the range of measured heat flows (e.g., Studt and Thompson 1969;Thompson 1977Thompson , 1980. This heat flux is augmented within the rift in later models by addition of magmatic heat sources, as described in Sect.…”